U.S. patent application number 14/234519 was filed with the patent office on 2014-06-26 for system and method for implementing mains-signal-based dimming of solid state lighting module.
This patent application is currently assigned to KONINKLIJKE PHILIPS N.V.. The applicant listed for this patent is Kaustuva Acharya, Raman Nair Harish Gopala Pillai, Ajay Tripathi. Invention is credited to Kaustuva Acharya, Raman Nair Harish Gopala Pillai, Ajay Tripathi.
Application Number | 20140176008 14/234519 |
Document ID | / |
Family ID | 46968325 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140176008 |
Kind Code |
A1 |
Harish Gopala Pillai; Raman Nair ;
et al. |
June 26, 2014 |
SYSTEM AND METHOD FOR IMPLEMENTING MAINS-SIGNAL-BASED DIMMING OF
SOLID STATE LIGHTING MODULE
Abstract
A system for implementing mains-voltage-based dimming of a solid
state lighting module includes a transformer, a mains sensing
circuit and a processing circuit. The transformer includes a
primary side connected to a primary side circuit and a secondary
side connected to a secondary side circuit, the primary and second
side circuits being separated by an isolation barrier. The mains
sensing circuit receives a rectified mains voltage from the primary
side circuit and generates a mains sense signal indicating
amplitude of the rectified mains voltage. The processing circuit
receives the mains sense signal from the mains sensing circuit
across the isolation barrier, and outputs a dimming reference
signal to the secondary side circuit in response to the mains sense
signal. Light output by the solid state lighting module, connected
to the secondary side circuit, is adjusted in response to the
dimming reference signal output by the processing circuit.
Inventors: |
Harish Gopala Pillai; Raman
Nair; (Arlington Heights, IL) ; Acharya;
Kaustuva; (Bartlett, IL) ; Tripathi; Ajay;
(Libertyville, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Harish Gopala Pillai; Raman Nair
Acharya; Kaustuva
Tripathi; Ajay |
Arlington Heights
Bartlett
Libertyville |
IL
IL
IL |
US
US
US |
|
|
Assignee: |
KONINKLIJKE PHILIPS N.V.
EINDHOVEN
NL
|
Family ID: |
46968325 |
Appl. No.: |
14/234519 |
Filed: |
July 24, 2012 |
PCT Filed: |
July 24, 2012 |
PCT NO: |
PCT/IB2012/053755 |
371 Date: |
January 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61511245 |
Jul 25, 2011 |
|
|
|
Current U.S.
Class: |
315/291 |
Current CPC
Class: |
H05B 45/00 20200101;
H05B 45/37 20200101; H05B 45/50 20200101 |
Class at
Publication: |
315/291 |
International
Class: |
H05B 33/08 20060101
H05B033/08 |
Claims
1. A system for implementing mains-voltage-based dimming of a solid
state lighting module, the system comprising: a transformer
comprising a primary side connected to a primary side circuit and a
secondary side connected to a secondary side circuit, the primary
side circuit being separated from the secondary side circuit by an
isolation barrier; a mains sensing circuit configured to receive a
rectified mains voltage from the primary side circuit and to
generate a mains sense signal indicating amplitude of the rectified
mains voltage; and a processing circuit configured to receive the
mains sense signal from the mains sensing circuit across the
isolation barrier, and to output a dimming reference signal to the
secondary side circuit in response to the mains sense signal,
wherein light output by the solid state lighting module, connected
to the secondary side circuit, is adjusted in response to the
dimming reference signal output by the processing circuit.
2. The system of claim 1, further comprising a first optical
isolator configured to couple the processing circuit with the mains
sensing circuit across the isolation barrier.
3. The system of claim 2, further comprising an output current
control in the secondary side circuit configured to receive the
dimming reference signal, to compare the dimming reference signal
with a drive current of the solid state lighting module, and to
generate a dimming feedback signal based on a result of the
comparison.
4. The system of claim 3, further comprising: a second optical
isolator configured to couple the output current control with the
primary side circuit to enable transmission of the dimming feedback
signal to the primary side circuit, wherein the light output by the
solid state lighting module is adjusted in response to the dimming
feedback signal.
5. The system of claim 4, wherein solid state lighting module
comprises a plurality of light-emitting diodes (LEDs).
6. The system of claim 2, wherein the mains sense signal comprises
a pulse-width modulated (PWM) signal, and the mains sensing circuit
transmits the PWM signal to the processing circuit through the
first optical isolator.
7. The system of claim 6, wherein the mains sensing circuit
comprises a microcontroller configured to generate the PWM signal,
the microcontroller comprising an analog-to-digital converter (ADC)
configured to receive the rectified mains voltage.
8. The system of claim 3, wherein the mains sensing circuit
comprises: a resistive divider configured to receive the rectified
mains voltage from the voltage rectifier and to provide a divided
mains voltage; a clock configured to generate a clock signal; and a
pulse signal generator configured to generate the PWM signal based
on the divided mains voltage and the clock signal, wherein a width
of each pulse of the PWM signal is modulated by the amplitude of
the rectified mains voltage.
9. The system of claim 8, wherein the clock comprises a first 555
timer and the pulse signal generator comprises a second 555
timer.
10. The system of claim 1, wherein an amount of light output by the
solid state lighting module varies directly with the amplitude of
the rectified mains voltage.
11. The system of claim 1, wherein the solid state lighting module
comprises a retrofit light-emitting diode (LED) module configured
to replace a conventional magnetic ballast.
12. A method of providing mains-signal-based dimming of a
light-emitting diode (LED) module, the method comprising:
generating a mains sensing signal indicating amplitude of a
rectified mains voltage from a primary side circuit, connected to a
primary side of a power transformer; transmitting the mains sensing
signal across an isolation barrier corresponding to the power
transformer; generating a dimming feedback signal in a secondary
side circuit, connected to a secondary side of the power
transformer, based at least in part on the transmitted mains
sensing signal; transmitting the dimming feedback signal from the
secondary side circuit across the isolation barrier to the primary
side circuit; and adjusting a drive current of the LED module
output by the secondary side circuit based on the dimming feedback
signal transmitted to the primary side circuit.
13. The method of claim 12, wherein generating the dimming feedback
signal comprises: generating a dimming reference signal based at
least in part on the transmitted mains sensing signal; providing
the dimming reference signal to the secondary side circuit;
comparing the dimming reference signal with at least one electrical
condition in the secondary side circuit; and generating the dimming
feedback signal to indicate a result of the comparison.
14. The method of claim 12, wherein adjusting the drive current of
the LED module comprises: adjusting at least one of a primary side
voltage and a primary side current input to the primary side of the
power transformer based on the dimming feedback signal, which
results in a corresponding adjustment to at least one of a
secondary side voltage and a secondary side current of the
secondary side of the power transformer, wherein the drive current
is based on the secondary side current.
15. The method of claim 12, wherein the mains sense signal
comprises a pulse-width modulated (PWM) signal.
16. The system of claim 12, wherein the LED module comprises a
retrofit LED module configured to replace a magnetic ballast.
17. A mains-signal-based driver for dimming a light-emitting diode
(LED) module, the driver comprising: a transformer having a primary
side and a secondary side; a primary side circuit connected to the
primary side of the transformer, the primary side circuit
comprising a voltage rectifier configured to rectify a dimmed mains
voltage; a secondary side circuit connected to the secondary side
of the transformer and configured to output a drive current for
driving the LED module, the secondary side circuit comprising an
output current control, wherein the secondary side circuit is
separated from the primary side circuit by an isolation barrier;
and a dimming control circuit comprising a mains sensing circuit
configured to generate a mains sense signal indicating amplitude of
the rectified mains voltage; an optical isolator configured to
provide electrical coupling across the isolation barrier; and a
microprocessor configured to receive the mains sense signal from
the mains sensing circuit via the optical isolator, to generate a
current reference signal in response to the mains sense signal and
to output the current reference signal to the output current
control, wherein the output current control generates a dimming
feedback signal based on a comparison of the current reference
signal and the drive current, and transmits the dimming feedback
signal to the primary side circuit across the isolation barrier,
and wherein the primary side circuit adjusts an input to the
transformer in response to the dimming feedback signal, thereby
adjusting the drive current in the secondary side circuit.
18. The system of claim 17, wherein the mains sense signal
comprises a pulse-width modulated (PWM) signal, and the mains
sensing circuit transmits the PWM signal to the processing circuit
through the first optical isolator.
19. The system of claim 18, wherein the mains sensing circuit
comprises: a resistive divider configured to provide a divided
mains voltage from the rectified mains voltage; a clock configured
to generate a clock signal; and a pulse signal generator configured
to generate the PWM signal based on the divided mains voltage and
the clock signal, wherein a width of each pulse of the PWM signal
is modulated by the amplitude of the rectified mains voltage.
20. The system of claim 18, wherein the mains sensing circuit
comprises a microcontroller configured to generate the PWM signal,
the microcontroller comprising an analog-to-digital converter (ADC)
configured to receive the rectified mains voltage.
Description
TECHNICAL FIELD
[0001] The present invention is directed generally to control of
solid state lighting devices. More particularly, various inventive
methods and apparatus disclosed herein relate to implementing
mains-signal-based dimming of a solid state lighting module.
BACKGROUND
[0002] Digital lighting technologies, i.e., illumination based on
semiconductor light sources, such as light-emitting diodes (LEDs),
offer a viable alternative to traditional fluorescent, HID, and
incandescent lamps. Functional advantages and benefits of LEDs
include high energy conversion and optical efficiency, durability,
lower operating costs, and many others. Recent advances in LED
technology have provided efficient and robust full-spectrum
lighting sources that enable a variety of lighting effects in many
applications.
[0003] In order to retrofit LED module applications in conventional
outdoor light fixtures, the traditional mains-dimmable magnetic
ballast must be replaced, e.g., using an LED driver connected
between the mains voltage supply and the LED module. In order to
enable dimming of light output by the LEDs based on the mains
voltage (as is used in conventional magnetic dimming applications),
the LED driver senses the mains voltage and reduces the output
current based on the sensed voltage. The LED driver may include a
power transformer with primary side and secondary side circuits
separated by an isolation barrier. Therefore, information regarding
the dimmed mains voltage on the primary side of the isolation
barrier must be sent over the isolation barrier to a controller on
the secondary side of the isolation barrier.
[0004] Thus, there is a need in the art for a mains dimming
technique using simple circuitry for mains voltage sensing and
transmitting mains dimming information to a controller across an
isolation barrier.
SUMMARY
[0005] The present disclosure is directed to inventive apparatus
and method for mains dimming using circuitry for sensing dimmed
mains voltage on a primary side of an LED driver, and accurately
transmitting the dimmed mains voltage information to a controller
on a secondary side of the LED driver across an isolation barrier.
Using the dimmed mains voltage information, various schemes for
dimming LED module current may be implemented.
[0006] Generally, in one aspect, a system for implementing
mains-voltage-based dimming of a solid state lighting module
includes a transformer, a mains sensing circuit and a processing
circuit. The transformer includes a primary side connected to a
primary side circuit and a secondary side connected to a secondary
side circuit, the primary and second side circuits being separated
by an isolation barrier. The mains sensing circuit receives a
rectified mains voltage from the primary side circuit and generates
a mains sense signal indicating amplitude of the rectified mains
voltage. The processing circuit receives the mains sense signal
from the mains sensing circuit across the isolation barrier, and
outputs a dimming reference signal to the secondary side circuit in
response to the mains sense signal. Light output by the solid state
lighting module, connected to the secondary side circuit, is
adjusted in response to the dimming reference signal output by the
processing circuit.
[0007] In another aspect, a method of providing mains-signal-based
dimming of a light-emitting diode (LED) module includes generating
a mains sensing signal indicating amplitude of a rectified mains
voltage from a primary side circuit, connected to a primary side of
a power transformer; transmitting the mains sensing signal across
an isolation barrier corresponding to the power transformer;
generating a dimming feedback signal in a secondary side circuit,
connected to a secondary side of the power transformer, based at
least in part on the transmitted mains sensing signal. The dimming
feedback signal is transmitted from the secondary side circuit
across the isolation barrier to the primary side circuit. A drive
current of the LED module output by the secondary side circuit is
then adjusted based on the dimming feedback signal transmitted to
the primary side circuit.
[0008] In another aspect, a mains-signal-based driver for dimming
an LED module includes a transformer having a primary side and a
secondary side, a primary side circuit connected to the primary
side of the transformer, a secondary side circuit connected to the
secondary side of the transformer, and dimming control circuit. The
primary side circuit includes a voltage rectifier configured to
rectify a dimmed mains voltage. The secondary side circuit is
configured to output a drive current for driving the LED module,
and includes an output current control. The secondary side circuit
is separated from the primary side circuit by an isolation barrier.
The dimming control circuit includes a mains sensing circuit
configured to generate a mains sense signal indicating amplitude of
the rectified mains voltage; an optical isolator configured to
provide electrical coupling across the isolation barrier; and a
microprocessor configured to receive the mains sense signal from
the mains sensing circuit via the optical isolator, to generate a
current reference signal in response to the mains sense signal and
to output the current reference signal to the output current
control. The output current control generates a dimming feedback
signal based on a comparison of the current reference signal and
the drive current, and transmits the dimming feedback signal to the
primary side circuit across the isolation barrier. The primary side
circuit adjusts an input to the transformer in response to the
dimming feedback signal, thereby adjusting the drive current in the
secondary side circuit.
[0009] As used herein for purposes of the present disclosure, the
term "LED" should be understood to include any electroluminescent
diode or other type of carrier injection/junction-based system that
is capable of generating radiation in response to an electric
signal. Thus, the term LED includes, but is not limited to, various
semiconductor-based structures that emit light in response to
current, light emitting polymers, organic light emitting diodes
(OLEDs), electroluminescent strips, and the like. In particular,
the term LED refers to light emitting diodes of all types
(including semi-conductor and organic light emitting diodes) that
may be configured to generate radiation in one or more of the
infrared spectrum, ultraviolet spectrum, and various portions of
the visible spectrum (generally including radiation wavelengths
from approximately 400 nanometers to approximately 700 nanometers).
Some examples of LEDs include, but are not limited to, various
types of infrared LEDs, ultraviolet LEDs, red LEDs, blue LEDs,
green LEDs, yellow LEDs, amber LEDs, orange LEDs, and white
LEDs.
[0010] For example, one implementation of an LED configured to
generate essentially white light (e.g., a white LED) may include a
number of dies which respectively emit different spectra of
electroluminescence that, in combination, mix to form essentially
white light. In another implementation, a white light LED may be
associated with a phosphor material that converts
electroluminescence having a first spectrum to a different second
spectrum. In one example of this implementation,
electroluminescence having a relatively short wavelength and narrow
bandwidth spectrum "pumps" the phosphor material, which in turn
radiates longer wavelength radiation having a somewhat broader
spectrum.
[0011] It should also be understood that the term LED does not
limit the physical and/or electrical package type of an LED. For
example, as discussed above, an LED may refer to a single light
emitting device having multiple dies that are configured to
respectively emit different spectra of radiation (e.g., that may or
may not be individually controllable). Also, an LED may be
associated with a phosphor that is considered as an integral part
of the LED (e.g., some types of white LEDs). In general, the term
LED may refer to packaged LEDs, non-packaged LEDs, surface mount
LEDs, chip-on-board LEDs, T-package mount LEDs, radial package
LEDs, power package LEDs, LEDs including some type of encasement
and/or optical element (e.g., a diffusing lens), etc.
[0012] The term "light source" should be understood to refer to any
one or more of a variety of radiation sources, including, but not
limited to, LED-based sources (including one or more LEDs as
defined above).
[0013] A given light source may be configured to generate
electromagnetic radiation within the visible spectrum, outside the
visible spectrum, or a combination of both. Hence, the terms
"light" and "radiation" are used interchangeably herein.
Additionally, a light source may include as an integral component
one or more filters (e.g., color filters), lenses, or other optical
components. Also, it should be understood that light sources may be
configured for a variety of applications, including, but not
limited to, indication, display, and/or illumination. An
"illumination source" is a light source that is particularly
configured to generate radiation having a sufficient intensity to
effectively illuminate an interior or exterior space. In this
context, "sufficient intensity" refers to sufficient radiant power
in the visible spectrum generated in the space or environment (the
unit "lumens" often is employed to represent the total light output
from a light source in all directions, in terms of radiant power or
"luminous flux") to provide ambient illumination (i.e., light that
may be perceived indirectly and that may be, for example, reflected
off of one or more of a variety of intervening surfaces before
being perceived in whole or in part).
[0014] The term "lighting fixture" is used herein to refer to an
implementation or arrangement of one or more lighting units in a
particular form factor, assembly, or package. The term "lighting
unit" is used herein to refer to an apparatus including one or more
light sources of same or different types. A given lighting unit may
have any one of a variety of mounting arrangements for the light
source(s), enclosure/housing arrangements and shapes, and/or
electrical and mechanical connection configurations. Additionally,
a given lighting unit optionally may be associated with (e.g.,
include, be coupled to and/or packaged together with) various other
components (e.g., control circuitry) relating to the operation of
the light source(s). An "LED-based lighting unit" refers to a
lighting unit that includes one or more LED-based light sources as
discussed above, alone or in combination with other non LED-based
light sources. A "multi-channel" lighting unit refers to an
LED-based or non LED-based lighting unit that includes at least two
light sources configured to respectively generate different
spectrums of radiation, wherein each different source spectrum may
be referred to as a "channel" of the multi-channel lighting
unit.
[0015] The term "controller" is used herein generally to describe
various apparatus relating to the operation of one or more light
sources. A controller can be implemented in numerous ways (e.g.,
such as with dedicated hardware) to perform various functions
discussed herein. A "processor" is one example of a controller
which employs one or more microprocessors that may be programmed
using software (e.g., microcode) to perform various functions
discussed herein. A controller may be implemented with or without
employing a processor, and also may be implemented as a combination
of dedicated hardware to perform some functions and a processor
(e.g., one or more programmed microprocessors and associated
circuitry) to perform other functions. Examples of controller
components that may be employed in various embodiments of the
present disclosure include, but are not limited to, conventional
microprocessors, application specific integrated circuits (ASICs),
and field-programmable gate arrays (FPGAs).
[0016] In various implementations, a processor or controller may be
associated with one or more storage media (generically referred to
herein as "memory," e.g., volatile and non-volatile computer memory
such as RAM, PROM, EPROM, and EEPROM, floppy disks, compact disks,
optical disks, magnetic tape, etc.). In some implementations, the
storage media may be encoded with one or more programs that, when
executed on one or more processors and/or controllers, perform at
least some of the functions discussed herein. Various storage media
may be fixed within a processor or controller or may be
transportable, such that the one or more programs stored thereon
can be loaded into a processor or controller so as to implement
various aspects of the present invention discussed herein. The
terms "program" or "computer program" are used herein in a generic
sense to refer to any type of computer code (e.g., software or
microcode) that can be employed to program one or more processors
or controllers.
[0017] It should be appreciated that all combinations of the
foregoing concepts and additional concepts discussed in greater
detail below (provided such concepts are not mutually inconsistent)
are contemplated as being part of the inventive subject matter
disclosed herein. In particular, all combinations of claimed
subject matter appearing at the end of this disclosure are
contemplated as being part of the inventive subject matter
disclosed herein. It should also be appreciated that terminology
explicitly employed herein that also may appear in any disclosure
incorporated by reference should be accorded a meaning most
consistent with the particular concepts disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, emphasis instead generally
being placed upon illustrating the principles of the invention.
[0019] FIG. 1 is a simplified block diagram showing a driver for a
mains-signal-based, dimmable solid state lighting system, according
to a representative embodiment.
[0020] FIG. 2 is a simplified block diagram of an illustrative
mains sensing circuit, configured to generate a PWM signal,
according to a representative embodiment.
[0021] FIG. 3 is a simplified block diagram showing a driver for a
mains-signal-based, dimmable solid state lighting system, according
to a representative embodiment.
[0022] FIG. 4 is a flow diagram showing a process of
mains-signal-based dimming a solid state lighting load, according
to a representative embodiment.
[0023] FIG. 5 is a set of graphs illustrating simulation results of
a driver for a mains-signal-based, dimmable solid state lighting
system, according to a representative embodiment.
DETAILED DESCRIPTION
[0024] In the following detailed description, for purposes of
explanation and not limitation, representative embodiments
disclosing specific details are set forth in order to provide a
thorough understanding of the present teachings. However, it will
be apparent to one having ordinary skill in the art having had the
benefit of the present disclosure that other embodiments according
to the present teachings that depart from the specific details
disclosed herein remain within the scope of the appended claims.
Moreover, descriptions of well-known apparatuses and methods may be
omitted so as to not obscure the description of the representative
embodiments. Such methods and apparatuses are clearly within the
scope of the present teachings.
[0025] Applicants have recognized and appreciated that it would be
beneficial to provide a circuit capable of sensing dimmed mains
voltage on a primary side of an LED driver and transmitting
information regarding the sensed dimmed mains voltage over an
isolation barrier to a processor or controller on a secondary side
of the LED driver.
[0026] Mains-voltage-based dimming schemes are used, for example,
in magnetic ballasts of conventional lighting applications. When
retrofit LED modules are used to replace magnetic ballasts, it is
desirable that dimming continue to be performed using the mains
voltage, as well. According to mains-voltage-based dimming schemes,
the amount of light output is reduced as the mains voltage is
reduced, e.g., via a dimming controller. For LEDs, dimming is
achieved by changing an output current provided to the LEDs in
response to changes in the mains voltage, e.g., via the dimming
controller. Different mains voltage dimming schemes may be
implemented, such as bi-level dimming, in which the light output
switches between two levels depending on the level of the mains
voltage, and linear dimming, in which the light output decreases
linearly as the level of the mains voltage is reduced.
[0027] FIG. 1 is a simplified block diagram showing a driver for a
dimmable lighting system, according to a representative
embodiment.
[0028] Referring to FIG. 1, driver 100 for implementing
mains-voltage-based dimming of a solid state lighting module,
indicated as LED module 160, includes an isolating transformer 120
having a primary side connected to a primary side circuit 110 and a
secondary side connected to a secondary side circuit 140. For
example, the transformer 120 may be a high-frequency/high power
transformer, such that isolation may be achieved when the LED
module 160 is implemented as a high brightness LED module. The
primary side circuit 110 receives a dimmed mains voltage from mains
voltage source 101 via dimming controller 105, which may be sine
dimming controller, for example. As discussed in detail below, the
primary side circuit 110 includes a voltage rectifier (not shown in
FIG. 1) for receiving the dimmed mains voltage and providing
rectified mains voltage V.sub.R. The secondary side circuit 140 is
connected to the LED module 160, and outputs an adjustable drive
current I.sub.D to the LED module 160 based on primary side current
I.sub.pri and induced secondary side current I.sub.sec of the
transformer 120.
[0029] The driver 100 further includes dimming control circuit 130
connected to both the primary side circuit 110 and the secondary
side circuit 140 across isolation barrier 125, which corresponds to
the transformer 120. The dimming control circuit 130 includes mains
sensing circuit 132, isolator 134 and processing circuit 136. The
mains sensing circuit 132 is configured to receive rectified mains
voltage V.sub.R from the voltage rectifier in the primary side
circuit 110, and to generate mains sense signal MSS indicating the
amplitude of the rectified mains voltage V.sub.R. The mains sensing
circuit 132 transmits the mains sense signal MSS to the processing
circuit 136 across the isolation barrier 125 via the isolator 134.
The isolator 134 may be an optical isolator, for example, which
enables information (e.g., the mains sense signal MSS) to be
exchanged using light signals, while maintaining electrical
isolation across the isolation barrier 125. Thus, the isolator 134
may be implemented accurately using low cost bi-level
opto-isolators, for example. In alternative embodiments, coupling
across the isolation barrier 125 may be obtained using other types
of isolation, such as transformers, without departing from the
scope of the present teachings.
[0030] The processing device 136 is located across the isolation
barrier 125 from the primary side circuit 110 because the
processing device 136 senses signals from the LED module 160, as
well as other dimming controllers (not shown) and provides
supervisory reference commands to the secondary circuit 140, as
discussed below. For example, in the depicted configuration, the
processing circuit 136 receives the mains sense signal MSS from the
mains sensing circuit 132 and outputs one or more dimming reference
signals to the secondary side circuit 140, determined at least in
part based on the mains sense signal MSS. The dimming reference
signals may include a current reference signal I.sub.ref and/or a
voltage reference signal V.sub.ref, for example, as discussed
below. The processing circuit 136 may also receive a dimming
control signal, indicating a set dimming level, and one or more LED
feedback signals from the LED module 160, including light level,
temperature, and the like. The dimming reference signals are
generated by the processing circuit 136 in response to at least the
mains sense signal MSS, and in various embodiments, also in
response to the dimming control signal and/or the LED feedback
signals.
[0031] The secondary side circuit 140 receives the dimming
reference signals, and compares the dimming reference signals with
corresponding electrical conditions. The secondary side circuit 140
generates a dimming feedback signal DFS based on the results of the
comparison, and transmits the dimming feedback signal DFS to the
primary side circuit 110 across the isolation barrier 125, e.g.,
via another isolator (not shown in FIG. 1). For example, when the
dimming control signals include current reference signal I.sub.ref,
an output current control (not shown) of the secondary side circuit
140 compares the current reference signal I.sub.ref with the drive
current I.sub.D being supplied to the LED module 160. The secondary
side circuit 140 then generates a dimming feedback signal DFS that
indicates the difference, if any, between the reference signal
I.sub.ref and the drive current I.sub.D.
[0032] The dimming feedback signal DFS is transmitted to the
primary side circuit 110 across the isolation barrier 125 via
another isolator (not shown in FIG. 1). In response to the dimming
feedback signal DFS, the primary side circuit 110 adjusts a primary
side voltage V.sub.pri input to the primary side of the transformer
120, as needed, which in turn adjusts a secondary voltage V.sub.sec
through the secondary side of the transformer 120 and thus the
drive current I.sub.D output by the secondary circuit 140 to the
LED module 160. Accordingly, the drive current I.sub.D drives the
LED module 160 to provide the amount of light corresponding to the
setting of the dimming controller 105. In an embodiment, the
processing circuit 136 may also provide a power control signal PCS
to the primary side circuit 110 across the isolation barrier 125
via another isolator (not shown in FIG. 1), which selectively
controls application of power to the primary side circuit 110 and
the secondary side circuit 140, as discussed below with reference
to FIG. 4.
[0033] In various embodiments, the processing circuit 136 may be
implemented as a controller or microcontroller, for example,
including a processor or central processing unit (CPU), application
specific integrated circuits (ASICs), field-programmable gate
arrays (FPGAs), or combinations thereof, using software, firmware,
hard-wired logic circuits, or combinations thereof. When using a
processor or CPU, a memory (not shown) is included for storing
executable software/firmware and/or executable code that controls
operations of the processing circuit 136. The memory may be any
number, type and combination of nonvolatile read only memory (ROM)
and volatile random access memory (RAM), and may store various
types of information, such as computer programs and software
algorithms executable by the processor or CPU. The memory may
include any number, type and combination of tangible computer
readable storage media, such as a disk drive, an electrically
programmable read-only memory (EPROM), an electrically erasable and
programmable read only memory (EEPROM), a CD, a DVD, a universal
serial bus (USB) drive, and the like.
[0034] In an embodiment, the mains sense signal MSS output by the
mains sensing circuit 132 is a pulse-width modulated (PWM) signal,
which is transmitted to the processing circuit 136 through the
isolator 134. The mains sensing circuit 132 may generate the PWM
signal in a variety of ways. For example, FIG. 2 is a simplified
block diagram of a mains sensing circuit, configured to generate a
PWM signal, according to a representative embodiment.
[0035] Referring to FIG. 2, the mains sensing circuit 132 includes
resistive divider 236, clock 237 and pulse signal generator 238.
The resistive divider 236 is configured to receive the rectified
mains voltage V.sub.R from the voltage rectifier in the primary
side circuit 110, and to provide a divided mains voltage to the
pulse signal generator 238. The clock 237 is configured to generate
a clock signal Clk, which is also provided to the pulse signal
generator 238. The pulse signal generator 238 thus generates a PWM
signal as the mains sense signal MSS, based on the divided mains
voltage and the clock signal Clk, such that a width of each pulse
of the PWM signal is modulated by the amplitude of the rectified
mains voltage V.sub.R. In an illustrative configuration, the clock
236 includes a first 555 timer and the pulse signal generator 238
includes a second 555 timer, for example, for generating the PWM
signal.
[0036] Of course, other configurations of the mains sensing circuit
132 and/or the various components thereof may be incorporated
without departing from the scope of the present teachings. For
example, in an alternative embodiment, the mains sensing circuit
132 may be implemented as a microcontroller configured to generate
the PWM signal. The microcontroller may include an
analog-to-digital converter (ADC) configured to receive the
rectified mains voltage V.sub.R from the voltage rectifier in the
primary side circuit 110, and to provide the PWM signal in
response. The microcontroller may also communicate with the
secondary side circuit 140 using some form digital communication
protocol, such as I2C or UART. The microcontroller may be a STM8S,
available from ST, for example, although other types of
microcontrollers may be incorporated without departing from the
scope of the present teachings.
[0037] FIG. 3 is a flow diagram showing a process of dimming a
solid state lighting load using mains dimming, according to a
representative embodiment. The illustrative steps of FIG. 3 may be
implemented by the driver 100 of FIG. 1, for example, although the
steps may be implemented by any system having similar capabilities,
without departing from the scope of the present teachings.
[0038] Referring to FIGS. 1 and 3, a rectified mains voltage
V.sub.R from primary side circuit 110 is received by mains sensing
circuit 132 at step S311. The mains sensing circuit 132 generates
mains sensing signal MSS at step S312, which indicates amplitude of
the rectified mains voltage V.sub.R. The mains sensing signal MSS
may be a PWM signal, for example, where the pulse widths are varied
to correspond to the amplitude of the rectified mains voltage
V.sub.R. At step S313, the mains sensing signal MSS is transmitted
across an isolation barrier, e.g, via isolator 134, to processing
circuit 136.
[0039] At step S314, the processing circuit 136 generates one or
more dimming reference signals based, at least in part, on the
mains sensing signal MSS received from the mains sensing circuit
132. The dimming reference signals are provided the secondary side
circuit 140 at step S315. For example, the dimming reference
signals may include a current reference signal I.sub.ref and/or a
voltage reference signal V.sub.ref, which are respectively provided
to an output current control and an output voltage control of the
secondary side circuit 140. At step S316, the dimming reference
signals are compared to corresponding electrical conditions of the
secondary side circuit 140, and a dimming feedback signal DFS is
generated at step S317 indicating the results of the comparison.
For example, the current reference signal I.sub.ref would be
compared to the drive current I.sub.D and the voltage reference
signal V.sub.ref would be compared to the drive voltage V.sub.D
driving the LED module 160. The dimming feedback signal DFS is
transmitted to the primary side circuit 110 across the isolation
barrier 125, e.g., via another isolator, at step S318. In response,
at step S319, the primary side circuit 110 is able to make
appropriate adjustments to the input, e.g., the primary side
voltage V.sub.pri and/or the primary current I.sub.pri, of the
primary side of the transformer 120, causing corresponding
adjustments to the drive current I.sub.D and/or drive voltage
V.sub.D output by the secondary side circuit 140 to the LED module
160. Accordingly, the LED module 160 is driven to provide the
appropriate amount of light corresponding to the setting of the
dimming controller 105.
[0040] FIG. 4 is a simplified block diagram showing a more detailed
driver for a dimmable lighting system, according to a
representative embodiment.
[0041] Referring to FIG. 4, driver 400 for implementing
mains-voltage-based dimming of a solid state lighting module,
indicated as illustrative LED module 460, includes an isolating
transformer 420 having a primary side connected to a primary side
circuit 410 and a secondary side connected to a secondary side
circuit 440. The primary side circuit 410 receives dimmed mains
voltage from mains voltage source 401 via dimming controller 405,
which may be a sine dimming controller, for example. The secondary
side circuit 440 is connected to the LED module 460, and outputs an
adjustable drive current I.sub.D to the LED module 460 based on
primary side current I.sub.pr, of the transformer 420, as discussed
below. The driver 400 further includes dimming control circuit 430
connected to both the primary side circuit 410 and the secondary
side circuit 440 across isolation barrier 425, which corresponds to
the transformer 420. The dimming control circuit 430 includes mains
sensing circuit 432, first optical isolator 434 and microprocessor
436, discussed below.
[0042] The primary side circuit 410 includes voltage rectifier 411,
boost power factor correction (PFC) circuit 412, boost control
circuit 413, PWM half-bridge converter 414, and PWM half-bridge
control stage 415. The voltage rectifier 411, and an EMI filter, is
connected to the dimming controller 405. The voltage rectifier 411
therefore receives the dimmed mains voltage from the mains voltage
source 401, and outputs rectified mains voltage V.sub.R (and
corresponding rectified mains current I.sub.R), thereby converting
the AC mains voltage into a rectified sinusoidal waveform. The
rectification is needed to create a constant DC voltage via the
boost PFC circuit 412, discussed below. The EMI filter may include
a network of inductors and capacitors (not shown) that limit the
high frequency components injected into the line.
[0043] The rectified mains voltage V.sub.R is provided to the boost
PFC circuit 412, which converts the rectified sinusoidal waveform
of the rectified mains voltage V.sub.R to a fixed, regulated DC
voltage, indicated as boosted voltage V.sub.B (and corresponding
rectified boosted current I.sub.B). In addition, the boost PFC
circuit 412 ensures that the rectified mains current I.sub.R drawn
from the voltage rectifier 411 and input to the boost PFC circuit
412 is in phase with the rectified mains voltage V.sub.R. This
ensures that the driver 400 operates close to unity power factor.
The boost control circuit 413 controls the switches of a boost
converter in the boost PFC circuit 412 accordingly.
[0044] The PWM half-bridge converter 414 converts the DC boosted
voltage V.sub.B received from the boost PFC circuit 412 to a
high-frequency pulsating signal, primary side voltage V.sub.pri
(and corresponding pulsed primary side current I.sub.pri), under
control of the PWM half-bridge control stage 415. The primary side
voltage V.sub.pri may be a PWM signal, for example, having a pulse
width set by operation of switches (not shown) in the PWM
half-bridge converter 414. The primary side voltage V.sub.pri is
applied to the primary side (primary winding) of the transformer
420. The PWM half-bridge control stage 415 determines the pulse
width of the primary side voltage V.sub.pri to be implemented by
the PWM half-bridge converter 414 based on a dimming feedback
signal DFS received from at least one of output current control 444
and output voltage control 446 of the secondary circuit 440, as
discussed below.
[0045] Secondary side voltage V.sub.sec (and corresponding
secondary side current I.sub.sec) is induced in the secondary side
(secondary winding) of the transformer 420 by the primary side
voltage V.sub.pri. The secondary side voltage V.sub.sec is
rectified and high-frequency filtered by output rectifier/filter
circuit 442 included in the secondary side circuit 440 to obtain
the desired drive voltage V.sub.D and corresponding drive current
I.sub.D for driving the LED module 360. The magnitude of the drive
current I.sub.D in particular dictates the illumination level of
the one or more LEDs in the LED module 460.
[0046] The secondary side circuit 440 further includes output
current control 444 and output voltage control 446. The output
current control 444 compares the drive current I.sub.D with a
current reference signal I.sub.ref output by the microprocessor 436
to obtain a current difference .DELTA.I, and the output voltage
control 446 compares the drive voltage V.sub.D with a voltage
reference signal V.sub.ref also output by the microprocessor 436 to
obtain a voltage difference .DELTA.V. A drive compensator (not
shown) determines the dimming feedback signal DFS based on at least
one of the current difference .DELTA.I and the voltage difference
.DELTA.V. The microprocessor 436 determines the values of the
current and voltage reference signals I.sub.ref and V.sub.ref based
on the mains sense signal MSS received from the mains sensing
circuit 432, discussed below, which in turn is based on the dimming
level set at the dimming controller 405.
[0047] The output current control 444 may also receive a softstart
signal (short pulse) from the microprocessor 436, which saturates
the current control loop via output current control 444. After the
softstart signal goes low, the current reference signal I.sub.ref
from the microprocessor 436 is gradually increased in order to
avoid flicker in the output LED current. During startup, the
current difference .DELTA.I may be determined as the current
reference signal I.sub.ref less the drive current I.sub.D and the
softstart signal, and the voltage difference .DELTA.V may be
determined as the voltage reference signal V.sub.ref less the drive
voltage V.sub.D and the softstart signal.
[0048] As mentioned above, the dimming feedback signal DFS
indicates both the current difference .DELTA.I and the voltage
difference .DELTA.V provided by the output current control 444 and
the output voltage control 446, respectively. In an embodiment,
only the current loop (using the current difference .DELTA.I) is
typically active. If output voltage goes beyond a predefined limit,
the voltage loop (using the voltage difference .DELTA.V) may be
used to reduce output current through the dimming feedback signal
DFS. The dimming feedback signal DFS is provided from the secondary
side circuit 440 to the PWM half-bridge control stage 415 across
the isolation barrier 425 via the second optical isolator 424
(which may be the same as or different than the first optical
isolator 434). The dimming feedback signal DFS thus controls the
PWM half-bridge converter 414 to adjust the pulse width of the
primary side voltage V.sub.pri based on dimming feedback signal
DFS. For example, if the drive current I.sub.D exceeds the current
reference signal I.sub.ref, as indicated by the dimming feedback
signal DFS, the PWM half-bridge control stage 415 will control the
PWM half-bridge converter 414 to reduce the primary side voltage
V.sub.pri, and thus the primary current I.sub.pri as well, for
example, by reducing the pulse width of the same. The change in the
primary side voltage V.sub.pri is reflected in a corresponding
change in the secondary voltage V.sub.sec, as well as the drive
voltage V.sub.D and the drive current I.sub.D output by the driver
400 for driving the LED module 460. Thus, the PWM half-bridge
control stage 415 is able to regulate the drive voltage V.sub.D
and/or the drive current I.sub.D of the driver 400 to a certain
value. Under normal steady-state operation, the current reference
signal I.sub.ref from the microprocessor 436 depends on the desired
dim level, as indicated by the mains sense signal MSS.
[0049] The boosted voltage V.sub.B output by the boost PFC circuit
412 is also provided to power supply 427, which may be a step down
DC-DC converter, such as a Viper power supply, for example. The
power supply 427 may step down the boosted voltage V.sub.B to a
lower voltage, such as 18V. The primary side of the power supply
427 is configured to selectively provide a regulated voltage to the
various components of the primary side circuit 410 (e.g., voltage
rectifier 411, boost PFC circuit 412, boost control circuit 413,
PWM half-bridge converter 414, PWM half-bridge control stage 415)
under control of switch 417. The operation and timing of the switch
417 (On/Off) is determined by power control signal PCS output by
the microprocessor 436, and received by the switch 417 across the
isolation barrier 425 via third optical isolator 428 (which may be
the same as or different than the first and second optical
isolators 434, 424). The secondary side of the power supply 427 is
configured to provide a regulated voltage to the various components
of the secondary side circuit 440 (e.g., output rectifier/filter
circuit 442, output current control 444, output voltage control
446). In an illustrative configuration, the power supply 27 may be
a flyback converter with two isolated outputs: one for the primary
side and one for the secondary side.
[0050] The driver 400 further includes dimming control circuit 430
connected to both the primary side circuit 410 and the secondary
side circuit 440 across isolation barrier 425, which corresponds to
the transformer 420. The dimming control circuit 430 includes mains
sensing circuit 432, first optical isolator 434 and microprocessor
436. As discussed above, the mains sensing circuit 432 is
configured to receive the rectified mains voltage V.sub.R from the
voltage rectifier 411, and to generate the mains sense signal MSS
indicating the amplitude of the rectified mains voltage V.sub.R.
The mains sensing circuit 432 transmits the mains sense signal MSS
to the microprocessor 436 across the isolation barrier 425 via the
first optical isolator 434. The mains sensing circuit 432 may be
implemented in a variety of configurations, including a pulse
signal generator (e.g., as discussed above with reference to FIG.
2) or a microcontroller.
[0051] The microprocessor 436 is configured to receive the mains
sense signal MSS from the mains sensing circuit 432 and to
determine the current reference signal I.sub.ref and the voltage
reference signal V.sub.ref in response. In addition, the
microprocessor 436 is configured to receive a dimming signal from
dimming input 454 through dimming control interface 455, where the
dimming signal indicates the desired level of dimming, e.g., set by
the user. For example, the dimming input 454 may provide a dimming
scale from 1V to 10V, where 1V indicates maximum dimming (lowest
level of output light) and 10V indicates minimum or no dimming
(highest level of output light). The microprocessor 436 may receive
multiple dimming level inputs, including the dimming input 454 and
the dimming controller 405, and sets current reference signal
I.sub.ref and/or the voltage reference signal V.sub.ref in
response. In an embodiment, the microprocessor 436 linearly
translates the mains sense signal MSS to obtain the current
reference signal I.sub.ref, for example, although the translation
may be bi-level, logarithmic, any predefined set of table values,
etc. The microprocessor 436 also receives feedback from the LED
module 460, e.g., via negative temperature coefficient (NTC)
sensing circuit 451 and RSET sensing circuit 452. The NTC sensing
circuit 451 senses the temperature of the LED module 460, and the
RSET sensing circuit 452 senses the value of an external resistor
which also sets the reference current I.sub.ref.
[0052] In addition, the microprocessor 436 generates the power
control signal PCS, which is a low level switch signal used to turn
ON/OFF the primary side supply and hence the LED driver 400. For
example, the power control signal PCS may be used to turn OFF the
LED driver 400 when a standby command is received from an external
input. A specific value of the mains sense signal MSS may also
signify a standby command. The power control signal PCS is sent by
the microprocessor 436 to the primary side circuit 410 across the
isolation barrier 425 via the third optical isolator 428 to operate
the switch 417, discussed above.
[0053] FIG. 5 is a set of graphs illustrating simulation results of
a driver for a dimmable solid state lighting system, according to a
representative embodiment. In particular, graph 5(c) shows
rectified mains voltage V.sub.R output by a voltage rectifier
(e.g., voltage rectifier 411) in the primary side circuit. Graphs
5(a) and 5(b) respectively show the sensed signal and the
corresponding PWM signal output by the mains sensing circuit (e.g.,
mains sensing circuit 432) as mains sense signal MSS in response to
the rectified mains voltage V.sub.R. The mains sense signal MSS is
provided to a processing circuit (e.g., microprocessor 436) across
an isolation barrier (e.g., isolation barrier 425) for determining
dimming feedback signal DFS. As shown in FIG. 5, the rectified
mains voltage V.sub.R is transmitted accurately over the isolation
barrier.
[0054] The mains-signal-based, dimmable solid state lighting system
driver discussed above may be applied to retrofit LED applications,
where it is desired to control the light output based on the mains
voltage signal. For example, the mains-signal-based, dimmable solid
state lighting system driver may be used for applications in which
the LED modules are replacing traditional magnetic ballasts.
[0055] While several inventive embodiments have been described and
illustrated herein, those of ordinary skill in the art will readily
envision a variety of other means and/or structures for performing
the function and/or obtaining the results and/or one or more of the
advantages described herein, and each of such variations and/or
modifications is deemed to be within the scope of the inventive
embodiments described herein. More generally, those skilled in the
art will readily appreciate that all parameters, dimensions,
materials, and configurations described herein are meant to be
exemplary and that the actual parameters, dimensions, materials,
and/or configurations will depend upon the specific application or
applications for which the inventive teachings is/are used. Those
skilled in the art will recognize, or be able to ascertain using no
more than routine experimentation, many equivalents to the specific
inventive embodiments described herein. It is, therefore, to be
understood that the foregoing embodiments are presented by way of
example only and that, within the scope of the appended claims and
equivalents thereto, inventive embodiments may be practiced
otherwise than as specifically described and claimed. Inventive
embodiments of the present disclosure are directed to each
individual feature, system, article, material, kit, and/or method
described herein. In addition, any combination of two or more such
features, systems, articles, materials, kits, and/or methods, if
such features, systems, articles, materials, kits, and/or methods
are not mutually inconsistent, is included within the inventive
scope of the present disclosure.
[0056] All definitions, as defined and used herein, should be
understood to control over dictionary definitions, definitions in
documents incorporated by reference, and/or ordinary meanings of
the defined terms.
[0057] The indefinite articles "a" and "an," as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to mean "at least one."
[0058] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Multiple elements listed with "and/or" should be construed in the
same fashion, i.e., "one or more" of the elements so conjoined.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified. As used herein
in the specification and in the claims, "or" should be understood
to have the same meaning as "and/or" as defined above.
[0059] As used herein in the specification and in the claims, the
phrase "at least one," in reference to a list of one or more
elements, should be understood to mean at least one element
selected from any one or more of the elements in the list of
elements, but not necessarily including at least one of each and
every element specifically listed within the list of elements and
not excluding any combinations of elements in the list of elements.
This definition also allows that elements may optionally be present
other than the elements specifically identified within the list of
elements to which the phrase "at least one" refers, whether related
or unrelated to those elements specifically identified. Thus, as a
non-limiting example, "at least one of A and B" (or, equivalently,
"at least one of A or B," or, equivalently "at least one of A
and/or B") can refer, in one embodiment, to at least one,
optionally including more than one, A, with no B present (and
optionally including elements other than B); in another embodiment,
to at least one, optionally including more than one, B, with no A
present (and optionally including elements other than A); in yet
another embodiment, to at least one, optionally including more than
one, A, and at least one, optionally including more than one, B
(and optionally including other elements); etc.
[0060] It should also be understood that, unless clearly indicated
to the contrary, in any methods claimed herein that include more
than one step or act, the order of the steps or acts of the method
is not necessarily limited to the order in which the steps or acts
of the method are recited. Also, reference numerals appearing in
the claims, if any, are provided merely for convenience and should
not be construed as limiting in any way.
[0061] In the claims, as well as in the specification above, all
transitional phrases such as "comprising," "including," "carrying,"
"having," "containing," "involving," "holding," "composed of," and
the like are to be understood to be open-ended, i.e., to mean
including but not limited to. Only the transitional phrases
"consisting of" and "consisting essentially of" shall be closed or
semi-closed transitional phrases, respectively.
* * * * *